1. Field of the Invention
The present invention is directed to a computer system and method for managing memory in a surveillance system. More particularly, it is directed to managing memory in a video surveillance system. Especially, it is directed to managing memory in such a system when the memory becomes fill or overflows.
2. Background of the Related Art
Surveillance systems are known in the art. In its simplest form, a surveillance system might essentially consist of an analog video camera hooked up to a remote video monitor as shown in FIG. 1A, or an audio device hooked to a speaker, although the camera may also contain audio as well. Using the camera for purposes of this discussion, the camera is pointed at a spot of interest, e.g., a front door, an automated teller machine, etc., and provides an image of that scene to the monitor. An operator watches the monitor to look for unusual or unauthorized behavior at the scene. If such activity is perceived, the operator takes appropriate action—identifying the individual, notifying security police, etc.
The system may have one or many cameras, each of which can be displayed in a predetermined area of the monitor. Alternatively, the operator may toggle through the scenes. Further, instead of one or more analog cameras, the system may use digital cameras such as CCD cameras and the like. Such digital cameras have the advantage of providing a high-quality, low-noise image when compared to analog images.
Another possible video surveillance arrangement is shown in FIG. 1B. This system uses multiple cameras connected to the monitor via a controller. The controller can multiplex several camera signals and provide them to the monitor. Also, it can control the positions of the cameras. The operator uses an input device such as a keyboard, joystick or the like to direct the controller to control the motion of the cameras so they point to particular areas within their range, track interesting features in the images, etc. It may also use the input device to control the controller to direct the controller to provide particular ones of the camera signals to the monitor.
FIG. 1C shows another arrangement of a video surveillance system. Here, a video recording device is connected to the camera outputs, the monitor input, or both. The video recording device, e.g., a video cassette recorder for analog cameras, can record the camera signals for archival, later review, and the like. Further, it can record images displayed on the monitor as evidence of activities taking place in the environments being inspected. For digital systems, the video storage device may be a digital storage device, a mass storage device such as a hard disk drive, or the like. When a hard disk drive is used, it may be a separate unit from the user controller and camera controller, or it may be part of an integrated system.
When the cameras are analog models, their signals may be stored on analog or digital storage devices. With an analog storage device or devices such as video cassette recorders, the camera signal or signals are stored on videotape much like a television signal. In a system using a digital storage device, e.g., a digital surveillance system or an analog camera system which digitizes the camera signal, the camera images are pixilated and stored in the digital storage device as data files. The files may be uncompressed, or they may be compressed using a compression algorithm to maximize use of the storage space.
If camera images are continually stored in a digital storage device without any deletions, eventually the storage device (or the part of it allocated for camera image storage) will become full. At that point, the stored data and incoming data must be managed to accommodate the new data.